Method for fabricating a semiconductor device

A method for fabricating a semiconductor device comprising a transistor including a control gate and a floating gate electrode, the method comprising the steps of:

• forming a first well of an impurity region of a first conductive type in a semiconductor substrate;
• forming a second well of an impurity region of a second conductive type in the first well;
• forming a control gate of an impurity region of the first conductive type in the second well;
• and
• forming a floating gate electrode on the semiconductor substrate containing an upper surface of the control gate with a gate insulation film therebetween,
• wherein in the step of forming a floating gate electrode, the floating gate electrode is formed with its upper surface covered with an insulation film.

A method for fabricating a semiconductor device comprising a transistor including a control gate and a floating gate electrode, the method comprising the steps of:

• forming a first well of an impurity region of a first conductive type in a semiconductor substrate;
• forming a second well of an impurity region of a second conductive type in the first well;
• forming a control gate of an impurity region of the first conductive type in the second well;
• and
• forming a floating gate electrode on the semiconductor substrate containing an upper surface of the control gate with a gate insulation film therebetween,
• the method further comprises, before the step of forming a control gate, the step of forming a threshold voltage control layer of the transistor in the semiconductor substrate, and another threshold voltage control layer of another transistor in the semiconductor substrate.

A method for fabricating a semiconductor device comprising a transistor including a control gate and a floating gate electrode, the method comprising the steps of:

• forming a first well of an impurity region of a first conductive type in a semiconductor substrate;
• forming a second well of an impurity region of a second conductive type in the first well;
• forming a control gate of an impurity region of the first conductive type in the second well;
• and
• forming a floating gate electrode on the semiconductor substrate containing an upper surface of the control gate with a gate insulation film therebetween,
• the method further comprises, after the step of forming a control gate, the step of implanting a dopant to form an impurity diffused layer in the semiconductor substrate by using a mask covering at least a region where the control gate and the floating gate electrode are opposed to each other.